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G M Hewitt

Publications and source records attributed to G M Hewitt.

At least 19 recordsLinked to original sources

The phylogeography of the darkling beetle, Hegeter politus, in the eastern Canary Islands.

We investigated the phylogeography of Hegeter politus, a saprophagous, flightless darkling beetle endemic to the eastern Canary Islands, using a fragment of the mitochondrial COI gene. Distance and parsimony based gene trees of the mitotypes identified revealed a striking association between mitotype clades and sampling locations. The branching order of the clades suggested that the colonization of the islands by Hegeter politus proceeded from the southern part of Fuerteventura in a north-northeast direction to Lanzarote and the smaller islands. Based on this, a colonization scenario compatible with the reported geological ages and volcanisms of the various parts of the islands has been proposed. The high divergence of the beetles collected from the extreme south of Fuerteventura (the Jandía peninsula) from all other samples has led us to propose that they may be from a new species that has not been described previously. The ecological isolation of Jandía from the rest of Fuerteventura by the sand dunes that cover its narrow isthmus in the north, and the existence of many plant and animal endemisms unique to Jandía, lend supportive evidence to our proposal. The similarities between the evolution of island endemics in the Hawaiian and Canary archipelagos have been discussed. We conclude that many endemics in the Canary archipelago, like the Hawaiian Islands, are most likely to have originated from post-colonization differentiation and divergence.

Animals

mtDNA phylogeography and postglacial patterns of subdivision in the meadow grasshopper Chorthippus parallelus.

A 300 bp portion of the mitochondrial cytochrome oxidase subunit I (COI) gene was used to investigate the intraspecific genetic structure of the European meadow grasshopper Chorthippus parallelus. Levels of genetic subdivision between geographical regions in Europe were assessed using the KST statistic and revealed patterns indicative of the postglacial history of this organism. Northern European populations are shown to share a very recent common ancestor with, and hence originate from, a Balkan expansion. Genetic distances between these areas and both southern Italy and central Spain are shown to be approximately equal, even though only the Spanish form is recognized as a distinct subspecies. Distance estimates indicate that the common ancestor of the two subspecies lived more than one glacial cycle ago, and the refugial populations have probably been diverging in isolation for five or six glacial cycles (approximately equal to 550,000 years). Comparisons are made to the analysis of a similar data set using an anonymous nuclear DNA marker (Cooper et al., 1995). Although the structure revealed is generally very similar, differences in the location of transition zones between different genetic forms of C. parallelus may reflect the different historical assortment of these molecules.

Animals

Chloroplast DNA recognizes three refugial sources of European oaks and suggests independent eastern and western immigrations to Finland.

Refugial differentiation and routes of postglacial migration are major determinants of the patterns of geographical variation we see in natural populations today. We used patterns of chloroplast DNA (cpDNA) variation to investigate the postglacial colonization history of the European oak species Quercus robur and Q. petraea. By sequencing two cpDNA segments using universal primers, we revealed four polymorphic sites which identify four cytotypes with characteristic geographical distributions. Of these, the principal eastern, central and western cytotypes divide the range into three longitudinal zones, each extending from the south to the north of Europe. This corroborates the idea that the postglacial colonization started from three distinct southerly refugia. The fourth cytotype, restricted to East Anglia, was probably derived from the western type postglacially. As a special problem, we addressed the controversial origin of Q. robur at its northern limits in south-western Finland, where it currently occupies a narrow coastal zone disjunct from the remaining oak range. Using a PCR-RFLP assay that discriminates the eastern cytotype, a contact zone of two cytotypes was identified in the region of the Salpausselkä ridges. This suggests that the marginal northern occurrence was independently colonized both from the east and from the west, across the Baltic Sea.

Chloroplasts

The phylogenetic relationships of seven European Ips (Scolytidae, Ipinae) species.

In Central Europe seven lps species are characterized by differences in morphology, structure of galleries, host specificity and aggressiveness. These species were analysed by allozyme markers and by sequencing 567 bp of the mitochondrial cytochrome oxidase I gene, in order to define their phylogenetic relationships. Orthotomicus erosus and Tomicus minor were taken as outgroup species. The data revealed high inter-specific and low intra-specific sequence divergence. Plotting the observed sequence divergence caused by transversions (Tv) and transitions (Ts) and the level of saturation for Ts and Tv of each codon position showed that the third positions were highly saturated by multiple substitutions. Maximum parsimony analysis produced two groups: (1) I. typographus, I. cembrae, I. amitinus, I. duplicatus and I. acuminatus; (2) I. mannsfeldi, I. sexdentatus and the two outgroups. In all analyses the species of the first cluster were put together and I. typographus and I. cembrae, and I. mannsfeldi and O. erosus emerged as sister pairs. The data do not support a common ancestor for the seven European lps species. The eight-spined bark beetles (except I. mannsfeldi) and I. acuminatus formed a monophyletic group. The close relationship of I. mannsfeldi and O. erosus supports the latter belonging to the genus lps as proposed by Wood (1982) and Escherich (1923). However, more genetic markers and more species of the genera Orthotomicus and Pityokteines have to be analysed to resolve the phylogenetic positions of I. sexdentatus I. mannsfeldi within the tribe lpinl.

Amylases

Polymorphic microsatellite loci in the European rabbit (Oryctolagus cuniculus) are also amplified in other lagomorph species.

Six polymorphic microsatellite markers developed for the European wild rabbit (Oryctolagus cuniculus) were amplified with 20 other species of lagomorphs, representing both commercially important species and species important from a conservation perspective. Successful amplification of a number of these loci has provided an important set of new molecular markers for this mammalian order.

Alleles

Assessment of the universality and utility of a set of conserved mitochondrial COI primers in insects.

A set of mitochondrial COI primers has been studied by genomic PCR and many primer combinations shown to work universally well across Insecta. They are able to amplify various amplicons with different variability which enables the selection of a particular amplicon as a suitable DNA marker for a project. The potential usefulness of different amplicons is examined, with analysis on published study cases employing these regions. With respect to their variability, amplicons UEA5/UEA6, UEA7/UEA8 and UEA5/UEA8 could be useful for low- to mid-level phylogenetic analysis, i.e. from species, genus to perhaps family level depending on taxa involved. UEA5/UEA6 will be too conserved for intraspecific studies. Amplicons UEA3/UEA4 and UEA9/UEA10 would be better suited to low-level phylogenetic investigations, such a analysis of relationships among closely related species and population genetic studies. However, these guidelines should not be over-generalized for the reasons given. Amplification conditions of various primer combinations, and general problems in the use of conserved PCR primers are discussed.

Conserved Sequence

Mitochondrial DNA sequence variation and phylogeography of Pimelia darkling beetles on the island of Tenerife (Canary Islands).

Four morphological taxa of the beetle genus Pimelia (Coleoptera, Tenebrionidae) are known to exist on the Atlantic island of Tenerife. We have obtained DNA sequences for 61 individuals from these taxa across the island for a 200 bp long fragment of the mitochondrial COI gene. In addition, a restriction site polymorphism in the nuclear rRNA ITS-1 sequence was identified and screened in a sample of these individuals using the enzyme Kpn2I. The results were analysed using approaches which allow inferences to be made about the population genetic structure and the mitochondrial genealogy of these closely related beetles. The mtDNA haplotype distribution and the estimates of sequence divergence revealed the presence of two ancient mtDNA lineages which coincide with the disjunct volcanic evolution of the island. The ITS-1 polymorphism was found to be diagnostic of these two lineages. However, the morphological and mitochondrial phylogenies were found to be discordant. We argue that this is possibly the result of rapid morphological change, produced by selection in different habitats, which has been recently superimposed on an older mitochondrial DNA divergence.

Animals

Phylogeny of the genus Hegeter (Tenebrionidae, Coleoptera) and its colonization of the Canary Islands deduced from Cytochrome Oxidase I mitochondrial DNA sequences.

The genus Hegeter comprises 23 species of darkling beetles (Tenebrionidae) endemic to the Macaronesian archipelagos, with 21 of them exclusive to the Canary Islands. We have sequenced 438 bp of the mitochondrial Cytochrome Oxidase I gene in 17 species (24 taxa) of Canarian Hegeter. Estimates of nucleotide composition, transition/transversion ratios and nucleotide change frequencies are very similar to those found in another tenebrionid Canarian genus Pimelia, indicating that similar molecular mechanisms are driving the sequence evolution. The sequence variation found allows phylogenetic analyses of the genus and the deduction of colonization patterns. These involve sequential island invasion with more rapid establishment and radiation than found in the related beetles of the genus Pimelia.

Animals

The sequence and structure of the meadow grasshopper (Chorthippus parallelus) mitochondrial srRNA, ND2, COI, COII ATPase8 and 9 tRNA genes.

The nucleotide sequence of the mitochondrial ND2, COI, COII, ATPase8, srRNA and nine tRNA genes have been sequenced from two individual of the meadow grasshopper Chorthippus parallelus. Comparisons are made to other insects for which the same regions are completely sequenced. Percentage A + T is found to be relatively low in C. parallelus though consistent with that of the other Orthopteran, Locusta migratoria. The relative number of substitutions observed in the different protein-coding genes was analysed between pairs of insect species sharing different levels of relatedness. A clear change in this rate was observed between the within-genus and between-genera comparisons. This change is interpreted in terms of the functional constraints acting on these four different genes. The patterns seem to result from an early saturation of COI and COII genes with synonymous substitutions, and a tolerance of ND2 and ATPase8 function to high levels of amino acid replacements. This analysis highlights a need for further sequence studies and comparisons between taxa of different levels of divergence in order to understand the patterns of mtDNA evolution on which many evolutionary investigations are based.

Adenosine Triphosphatases

The insect cytochrome oxidase I gene: evolutionary patterns and conserved primers for phylogenetic studies.

Insect mitochondrial cytochrome oxidase I (COI) genes are used as a model to examine the within-gene heterogeneity of evolutionary rate and its implications for evolutionary analyses. The complete sequence (1537 bp) of the meadow grasshopper (Chorthippus parallelus) COI gene has been determined, and compared with eight other insect COI genes at both the DNA and amino acid sequence levels. This reveals that different regions evolve at different rates, and the patterns of sequence variability seems associated with functional constraints on the protein. The COOH-terminal was found to be significantly more variable than internal loops (I), external loops (E), transmembrane helices (M) or the NH2 terminal. The central region of COI (M5-M8) has lower levels of sequence variability, which is related to several important functional domains in this region. Highly conserved primers which amplify regions of different variabilities have been designed to cover the entire insect COI gene. These primers have been shown to amplify COI in a wide range of species, representing all the major insect groups; some even in an arachnid. Implications of the observed evolutionary pattern for phylogenetic analysis are discussed, with particular regard to the choice of regions of suitable variability for specific phylogenetic projects.

Amino Acid Sequence

Highly conserved nuclear copies of the mitochondrial control region in the desert locust Schistocerca gregaria: some implications for population studies.

Animal mitochondrial DNA has proved a valuable marker in intraspecific systematic studies. However, if nucleotide sequence heterogeneity exists at the individual level, its usefulness will be much reduced. The study demonstrates that the presence of highly conserved non-coding mitochondrial sequences in the nuclear genome of Schistocerca gregaria greatly impairs the use of mtDNA in population genetic studies. Caution is called for in other organisms; and it seems necessary to check for conserved nuclear copies of mitochondrial sequences before launching into a large scale analysis of populations using mtDNA as a genetic marker. Experimental procedures are suggested for this purpose.

Animals

Mitochondrial DNA phylogeny and sequential colonization of Canary Islands by darkling beetles of the genus Pimelia (Tenebrionidae).

Fifteen species of the darkling beetle genus Pimelia (Tenebrionidae: Coleoptera) have been sequenced for a 365 b.p. portion of the mitochondrial Cytochrome Oxidase I gene. Thirteen of these are endemic species inhibiting the Canarian archipelago in the Atlantic and the other two are continental conspecifics. This data set has been phylogenetically analysed by maximum parsimony and distance approaches and the resulting trees used to deduce sequential interisland colonization. This suggests patterns compatible with the geological dating of the islands, but with increasing uncertainty when older events are considered. A colonization sequence from Fuerteventura to Tenerife followed by Tenerife to Gran Canarian and La Gomera, and from the latter to La Palma and then to El Hierro is proposed for the genus. A relatively recent secondary colonization from Gran Canaria to Gomera is deduced.

Animals

Evolution and structural conservation of the control region of insect mitochondrial DNA.

The control regions of mitochondrial DNA of two insects, Schistocerca gregaria and Chorthippus parallelus, have been isolated and sequenced. Their sizes are 752 bp and 1,512 bp, respectively, with the presence of a tandem repeat in C. parallelus. (The sequences of the two repeats are highly conserved, having a homology of 97.5%.) Comparison of their nucleotide sequences revealed the presence of several conserved sequence blocks dispersed through the whole control region, showing a different evolutionary pattern of this region in these insects as compared to that in Drosophila. A highly conserved secondary structure, located in the 3' region near the small rRNA gene, has been identified. Sequences immediately flanking this hairpin structure rather than the sequences of this structure themselves are conserved between S. gregaria/C. parallelus and Drosophila, having a sequence consensus of "TATA" at 5' and "GAA(A)T" at 3'. The motif "G(A)nT" is also present in the 3' flanking sequences of mammalian, amphibian, and fish mitochondrial L-strand replication origins and a potential plant mitochondrial second-strand-replication origin, indicating its universal conservation and functional importance related to replication origins. The stem-and-loop structure in S. gregaria/C. parallelus appears to be closely related to that found in Drosophila despite occupying a different position, and may be potentially associated with a second-strand-replication origin. This in turn suggests that such a secondary structure might be widely conserved across invertebrates while their location in the control region may be variable. We have looked for such a conserved structure in the control regions of two other insects, G. firmus and A. mellifera, whose DNA sequences have been published, and their possible presence is discussed. Mitochondrial control regions characterized to date in five different insect taxa (Drosophila, G. firmus, A. mellifera, S. gregaria, and C. parallelus) may be classed into two distinct groups having different evolutionary patterns. It is observed that tandem repetition of regions containing a probable replication origin occurred in some species from disjunct lineages in both groups, which would be the result of convergent evolution. We also discuss the possibility of a mechanism of "parahomologous recombination by unequal crossing-over" in mitochondria, which can explain the generation of such tandemly repeated sequences (especially the first critical repetition) in the control region of mtDNA, and also their convergent evolution in disjunct biological lineages during evolution.

Animals

Cloning and sequence analysis of an extremely homogeneous tandemly repeated DNA in the grasshopper Eyprepocnemis plorans.

Digestion of total nuclear DNA of the grasshopper Eyprepocnemis plorans with seven different restriction endonucleases (REs), and subsequent agarose gel electrophoresis, has shown the presence of highly repetitive DNA yielding the typical ladder-like banding pattern. The most clear pattern was produced by DraI, the monomer being some 180 bp. This repeat unit was subsequently cloned and sequenced. Bidirectional sequencing of five randomly chosen clones showed exactly the same nucleotides in all 180 positions. The possible explanations for such an extreme homogeneity of this tandem repeat are discussed in the light of current hypotheses on repetitive DNA function and molecular drive mechanisms.

Animals

Phylogeny of the Coleoptera based on mitochondrial cytochrome oxidase I sequence data.

A 400 base pair region of the mitochondrial cytochrome oxidase I gene (COI) was sequenced for thirty-seven species of beetle, representing fifteen families. The sequence was found to be highly variable, with 12-18% divergence within families, and up to 27% divergence between families. Phylogenetic analysis using the neighbour-joining method shows the Carabidae (Adephaga) as a distinct clade, but also shows that all other beetles (Polyphaga) diverged soon after the Adephaga/Polyphaga split. Whilst some species are grouped within their respective families, others are too diverged for easy resolution. The main disagreement with trees constructed using comparative morphology and the fossil record is the position of the Coccinellidae. Whilst COI may be an informative gene for molecular systematics at lower taxonomic levels, or in other insects, improved resolution of this particular phylogeny will require a more highly conserved sequence.

Amino Acid Sequence